Storage tanks



W. A. ROWLEY STORAGE TANKS' Nov. 21, 1967 5 Sheets-Sheet 1' Filed Dec. 27, 1965 INVENTOR W A Po w/ey BY 5 ATTORNEY Nov. 21, 1967 w. A. ROWLEY STORAGE TANKS Filed Dec. 27, 1965 3 Sheets-Sheet 2 INVENTQR W. A fiow/ey Nov. 21; 1967 w. A; ROWLEY 3,353,552

STORAGE TANKS Filed Dec. 27', 1965 5 Sheets-Sheet s INV ENTOE 8- MA. Wald LE) Q/MZ W ATTQQNE-Y United States Patent ABSTRACT OF THE DISCLOSURE A vessel for storing liquids comprising a bottom, an inner shell rising from the bottom, and an outer shell also rising from said bottom which surrounds and is spaced outwardly from the inner shell, the inner shell being of greater height than the outer shell, an inlet for v admitting fluid into the innermost of the chambers defined by the two shells, a passageway interconnecting those chambers, and a valve responsive to the level of liquid in the inner chamber which permits flow into the outer chamber when, but only when, the level in the inner chamber is below a predetermined level.

Containment vessels, or storage tanks, for liquids are usually constructed to design codes which limit the thickness of the plates used for the shell wall. There is consequently a limit to the size of a storage tank of conventional design which can be built from mild steel plates. Tanks of larger capacity can be built by using materials such as high tensile steel, but these are expensive.

The present invention provides a new construction in which the stresses induced in the lower courses by virtue of the head of liquid being stored are reduced, thus permitting the use of shells of lesser thickness or cheaper ..material than hitherto required for a given capacity, and

also making possible the manufacture of a storage tank of greater capacity than-hitherto possible with conventional designs.

The invention is defined in the appended claims, but

, in general terms a containment vessel in accordance with the invention comprises two shell walls of different diameters and heights disposed one within the other and attached to a common bottom, the larger diameter outer shell wall having a height about one-half that of the inner shell wall. Apart from their attachment, to the common bottom the two walls are not braced together, so that they can act independently to resist the hydrostatic pressures applied to them. The space within the inner shell wall constitutes an inner tank, which can be filled to one level, and the space between the two walls constitutes an outer tank, which can be filled to a second,

. lower level. Thehydrostatic load is shared between the two walls by controlling the relative liquid levels in the two tanks. The level of liquid in the outer tank is main-.

tained at about the second level whenever the liquid I level in the inner tank is above thesecond level; the

portion of the inner shell wall below the second level is then subjected to a hydrostatic load which is uniform throughout its height and is that resulting from the dif ference between the liquid levels in the two tanks, so that that lower portion of the inner wall can be made through out of the thickness necessary to withstand the maximum value of that uniform loading. To avoid inward pressure on the inner wall, the liquid level in the outer tank is not at any time allowed to become appreciably higher than the liquid level in the inner tank.

The required control of the relative liquid levels in the and outflow to the two tanks, but it is preferably effected automatically. Automatic control could be effected by providing one or more differential pressure sensing elements to operate similar valves controlling inflow and outflow to the two tanks. However, a preferable method is to connect the pipe or pipes for delivering and withdrawing liquid to the inner tank and to provide a passage connecting the inner tank to the outer tank, this passage being opened and closed by a valve operated by a float or other level sensing device.

The accompanying drawings show by way of example containment vessels in accordance with the invention provided with a variety of forms of such float-operated liquid level control systems. In these drawings, the size of the control means relative to the size of the vessel has been exaggerated for the sake of clarity, and the same reference numerals have been used to designate corresponding parts;

FIGURE 1 represents a vertical section through one form of vessel in accordance with the invention;

FIGURES 2, 3 and 4 represent similar sections through parts of three different alternative constructions;

FIGURE 5 represents a vertical section taken in a different plane; and

FIGURE 6 is a fragmentary section showing a modification of the construction of FIGURE 2.

Referring first to FIGURE 1, an inner shell wall 1 and an outer shell wall 2 are mounted on a common bottom 3. The inner tank 1 and the outer tank 4 (constituted by the space between the two walls) are interconnected by a pipe 5, which can be closed by a valve 6, pivotally mounted on a lever 7, which is pivoted to a fixed bracket 8. Lever 7 is coupled by a pivotally connected link 9 to an arm 10, which is pivoted to a fixed bracket 11 and carries a float 12. The arrangement is such that the valve 6 closes the entry to pipe 5 when the level in the inner tank rises to the maximum level of liquid in the outer tank, indicated by the dotted line 13, and remains closed as the liquid in the inner tank rises to any higher level. When the liquid level falls below 13, the float drops, opening valve 6, the travel of lever 7 being limited by a stop 21.

The outer tan-k 4 has a roof or cover 22 of flexible or other yielding construction and is provided with one or more overflow pipes 15, which may be open ended 01' may be fitted with pressure relief valves; in the latter case vapour pressure relief valves 16 may be fitted to be roof 22.

A pipe 17 for conveying liquid into or out of the inner tank passes through the outer tank. A flexible bellows 18 is attached to the outer shell 2 and to a flange on pipe 17. A stop valve 19 controlling liquid flow through pipe 17 is supported by a stool 20.

The interconnection between the inner and outer tanks must be of sufficient size to maintain the liquid levels in the two tanks substantially equal when the inner tank is being filled or emptied at the maximum rate. This can be I of failure of the tank due to malfunctioning of the level appropriate manipulation of valves controlling inflow control system.

In operation, assuming that both tanks are initially empty, the valve 6 is open with lever 7 resting against its stop 21. When the liquid enters the inner tank and the pipe 5 becomes submerged, liquid flows through it into the outer tank. The liquid levels in the inner and outer tanks rise together until the level 13 is reached, when float 12 rises and causes valve 6 to shut. As the liquid level in the inner tank continues to rise the liquid level in the outer tank remains at 13. When the level of liquid in the inner tank falls below 13, valve 6 opens and the liquid levels in inner and outer tanks fall together until the level in the inner tank falls below pipe 5. If it is desired to arrange for complete emptying of inner tank and annulus the ends of pipe 5, which can act as a syphon, are continued downwards into sumps in the bottom 3 (the valve 6, lever 7, and bracket 8 being housed in one of these sumps) and pipe 17 is similarly extended into a sump in the tank bottom.

In FIGURE 1, the inner tank 1 is shown open-topped, but it could be provided with a fixed roof of any construction, or with a floating roof. However, the use in conjunction with a floating roof of the level control system shown in FIGURE 1 presents difficulties in positioning the float 12, arm 10 and bracket 11 so as to allow the roof to rise and fall freely. FIGURE 2 shows a modified construction preferable for floating roof tanks. In this construction, the float 12 is disposed in a vertical guide tube 26, located in the outer tank 4 but connected to and supported by the inner tank 1 through valve housing 23, elbow 27 and branches 24 and 25. Float 12 is connected directly to rod 9 and is free to slide in the guide tube 26. The pipe of FIGURE 1 is replaced by the valve housing 23 and the fulcrum 8 of lever 7 now lies between valve 6 and rod 9. The interior of tank 1 is thus left entirely unobstructed by the level control'system, allowing free movement of the floating roof, indicated at 14. The method of operation is exactly the same as for the arrangement shown in FIGURE 1, except that the use of pipe 5 as a syphon is no longer possible.

FIGURE 3 shows an alternative arrangement, suitable for open-topped or fixed roof tanks, in which a level control system similar to that of FIGURE 2 is mounted inside the inner tank 1. The valve housing 23 is in this case carried on an inward facing branch 28, and the upper end of guide pipe 26 is left open and is supported by a bracket 29. The action of the system is exactly the same as for the system shown in FIGURE 2.

As an alternative to the level control systems already described which are all actuated by changes in liquid level in the inner tank it is possible to use a system which is actuated partly by changes in liquid level in the outer tank and partly by small differences in hydrostatic pressure between the outer and inner tanks. An example of such a I system is shown in FIGURE 4, in which the float 12 is in contact with the liquid in the outer tank 4 and rod 9 is pivotally connected to a cranked lever 30, pivoted on a fixed fulcrum 31, the lower end of lever 30 being pivotally connected to valve 6. The rod 9 slides in a guide 32 carried by a fixed bracket 33. When the liquid level in the outer tank is below its maximum level 13, the valve 6 is open, allowing liquid to flow between the inner tank and the annulus. When the liquid level in the outer tank rises to 13, the float rises and operates the lever 30 to pull valve 6 onto its seat. As the liquid level in the inner tank continues to rise, the liquid level in the outer tank remains at 13 and the difference in hydrostatic pressure presses valve 6 firmly against its seat. When the liquid level in the inner tank is reduced below 13 by a small amount, the difference in hydrostatic pressure on valve 6 opens it and the two tanks remain interconnected at lower liquid levels. By suitably proportioning the lengths of the arms of lever 30 and the buoyancy of float 12, valve 6 can be made to open automatically under the action of the small external hydrostatic pressure which the tank shell 1 can safely withstand.

It is necessary, or at least highly desirable, to provide safeguards against any departure from the correct operating conditions, which couldlead to failure of either of the inner or outer tank shells. In particular it is necessary to ensure that (a) the level of liquid in the outer tank is maintained at its maximum whenever the liquid in the inner tank is at a greater level; (b) the hydrostatic pressure in the inner tank wh n the level in it is at or near its maximum cannot be transmitted to the outer tank shell; and (c) the level of liquid in the outer tank will fall to substantially that of the liquid in the inner tank whenever the level in the inner tank is below the maximum level 13 for the outer tank. So long as no failure or malfunction occurs, these requirements are met by each of the level control systems described above, but additional features may be provided to safeguard against such failure or malfunction, as shown in FIGURE 5.

FIGURE 5 represents a section through part of a containment vessel in accordance with the invention, at a position remote from the level control system. The overflow pipe 15 for the outer tank, already described, is the fundamental safeguard against the transmission of inner tank pressure to the outer tank shell. The overflow is also a means of giving warning of leakage into the annulus. Additionally, there is provided a float operated level switch 34 which causes visual and/ or audible alarms to operate if the liquid level in the outer tank rises above the intended maximum 13 and before it reaches the overflow level.

In order to give Warning of low liquid level in the outer tank, which could occur in the event of loss of liquid from the annulus, a float operated level switch 35 is fitted at a level slightly below 13. In order that switch 35 shall not operate the alarm system unnecessarily when the liquid levels in both tanks are low, level switch 35 is linked in series with a similar level switch 36 which is responsive to the liquid level in the inner tank and is mounted at a. level slightly above 13. Level switches 34, 35 and 36 may operate electrically, pneumatically or in any other way. In FIGURE 5 level switch 36 is shown mounted in a housing 37 which is disposed in the outer tank but communicates' with the inner tank by its open end 38 and by small bore pipes 39 and 40. This is a standard method of mounting such a level switch on a floating roof tank. In the case of a tank without a floating roof, level switch 36 could be mounted directly on the shell of the inner tank in the same manner as level switches 34 and 35 are mounted on the outer tank.

Level switches 35 and 36 may be the known two way type and they may then be arranged to operate the alarm system in the event that the level in the annulus remains at or near 13, when the level in the inner tank is below 13, this function being additional to their function of giving warning of low liquid level in the outer tank, as described above. One or more pairs of level switches 35 and 36 may be used.

As a further safeguard against excessive pressure, either internal or external, on the inner tank shell a differential pressure cell 41 of known type, may be connected as shown between the inner tank and the outer tank at a point near to the bottom. The pipe connecting 41 to the inner tank passes through the outer tank shell 2 by means of a flexible bellows 42. This differential pressure cell may be adjusted to operate the alarm system before the limiting valves of both internal and external pressure on the inner tank shell are reached and it may also be arranged to give a continuous visual indication of the pressure on the inner tank shell at the level of the differential pressure cell. One or more of these differential pressure cells may be fitted as though desirable.

An alternative arrangement for the mounting of level switch 36 is shown in FIGURE 6, which shows a modified form of part of the construction of FIGURE 2, housing 37 taking the place of the elbow 27 shown in FIGURE 2.

What is claimed is:

1. A con-tainment vessel for liquids comprising an inner shell wall, an outer shell wall of lesser height than the inner shell wall which surrounds and is spaced outwardly from the lower part of the inner shell wall, a bottom to which the inner and outer shell walls are connected at their lower ends, the inner shell wall with the bottom defining an inner tank adapted to contain liquid up to a first given maximum level, the lower part of the inner shell wall with the bottom and the outer shell wall defining an outer tank adapted to contain liquid up to a second given maximum level which is lower than the first level, the inner and outer shell walls being free to yield independently of one another in response to the hydrostatic pressure of liquid in said inner and outer tanks, a pipe for the delivery and withdrawal of liquid communicating with the inner tank, a liquid passage connecting the inner tank to the outer tank, a valve for opening and closing said passage, and means operating automatically to open the valve when the level of liquid in the inner tank falls below said second level and to close the valve when the level of the liquid in the inner tank rises above said second level.

2. A vessel in accordance with claim 1 wherein said automatically operating means comprises a float responsive to the level of liquid in the inner tank and mechanical means coupling said float to the valve.

3. A vessel in accordance with claim 1 wherein said valve is exposed on opposite sides to the hydrostatic pressures in the inner and outer tanks, so that excess pressure in the inner tank will hold the valve closed and excess pressure in the outer tank will open the valve, and a float responsive to the level of liquid in the outer tank is mechanically coupled to the valve so as to close the valve when the level of liquid in the outer tank rises to said second level while permitting the valve to open in response to excess pressure in the outer tank when the level of liquid in the inner tank fall's a small distance below said second level.

4. A vessel in accordance with claim 1 wherein said pipe communicating with the inner tank passes through the outer shell wall and is flexibly sealed thereto.

5. A vessel in accordance with claim 1 in which the height above the bottom of said second level is approximately half that of said first level.

6. A vessel in accordance with claim 1 in which the outer tank is provided with an overflow pipe permitting liquid to escape from that tank if the liquid level in that tank unintentionally rises substantially above said second level.

7. A vessel in accordance with claim 1 and comprising automatically operating alarm systems for giving warning if the relative liquid levels in the inner and outer tanks depart from the conditions specified in claim 2.

8. A vessel for the bulk storage of a varying quantity of liquid comprising a supporting bottom, an inner shell Wall upstanding from said bottom to define with said bottom an inner tank, an outer shell wall also upstanding from the bottom at a position spaced outwardly from and surrounding said inner shell wall to define with the bottom and said inner shell wall an outer tank, said inner and outer shell walls being free to yield independently of one another in response to the hydrostatic pressure of liquid stored in said inner and outer tanks, pipes for the delivery and withdrawal of liquid communicating with the lower parts of said inner and outer tanks, means for sensing the level of liquid in said inner tank, and means responsive to said sensing means eifective whenever the level of liquid in said inner tank is above a particular level to maintain the level of liquid in said outer tank at about said particular level, and also effective whenever the level of liquid in said inner tank is below'said particular level to maintain the level of liquid in said outer tank no higher than the momentarily existing level of liquid in said inner tank.

References Cited UNITED STATES PATENTS 3,202,167 8/1965 De Young et a1. 137-264 X M. CARY NELSON, Primary Examiner. R. J. MILLER, Assistant Examiner. 

1. A CONTAINMENT VESSEL FOR LIQUIDS COMPRISING AN INNER SHELL WALL, AN OUTER SHELL WALL OF LESSER HEIGHT THAN THE INNER SHELL WALL WHICH SURROUNDS AND IS SPACED OUTWARDLY FROM THE LOWER PART OF THE INNER SHELL WALL, A BOTTOM TO WHICH THE INNER AND OUTER SHELL WALLS ARE CONNECTED AT THEIR LOWER ENDS, THE INNER SHELL WALL WITH THE BOTTOM DEFINING AN INNER TANK ADAPTED TO CONTAIN LIQUID UP TO A FIRST GIVEN MAXIMUM LEVEL, THE LOWER PART OF THE INNER SHELL WALL WITH THE BOTTOM AND THE OUTER SHELL WALL DEFINING AN OUTER TANK ADAPTED TO CONTAIN LIQUID UP TO A SECOND GIVEN MAXIMUM LEVEL WHICH IS LOWER THAN THE FIRST LEVEL, THE INNER AND OUTER SHELL WALLS BEING FREE TO YIELD INDEPENDENTLY OF ONE ANOTHER IN RESPONSE TO THE HYDROSTATIC PRESSURE OF LIQUID IN SAID INNER AND OUTER TANKS, A PIPE FOR THE DELIVERY AND WITHDRAWAL OF LIQUID COMMUNICATING WITH THE INNER TANK, A LIQUID PASSAGE CONNECTING THE INNER TANK TO THE OUTER TANK, A VALVE FOR OPENING AND CLOSING SAID PASSAGE, AND MEANS 